TiO2 nanocrystalline particles with monolayer adsorption of chlorin e6 trisodium salt (dye-TiO2 particles) were administered into a cancer cell, murine thymic lymphoma (EL-4). Irradiation of the polychromatic light (550-750 nm) that excites chlorin e6 significantly damaged the EL-4 cells. A higher cell-killing effect was found for the dye-TiO2 particle than for the system using chlorin e6 alone.